ServiceWorker: Make a way to retrieve a service worker version id (Blink)

Source/core/fetch/ResourceFetcher.cpp

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller (mueller@kde.org)
     Copyright (C) 2002 Waldo Bastian (bastian@kde.org)
     Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
     Copyright (C) 2009 Torch Mobile Inc. http://www.torchmobile.com/
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
     License as published by the Free Software Foundation; either
@@ skipping 606 matching lines @@
 bool ResourceFetcher::isControlledByServiceWorker() const
 {
     LocalFrame* localFrame = frame();
     if (!localFrame)
         return false;
     if (!m_documentLoader)
         return false;
     return localFrame->loader().client()->isControlledByServiceWorker(*m_documentLoader);
 }
 
+int64_t ResourceFetcher::serviceWorkerID() const
+{
+    LocalFrame* localFrame = frame();
+    if (!localFrame)
+        return -1;

[Mike West, 2014/10/28 08:09:24]

Why are you using -1 as the invalid value? Why not 0? 0 makes comparisons
simpler to understand, and would allow you to make this a `uint64_t` instead.
That would be less prone to breakage.

[nhiroki, 2014/10/28 08:34:01]

This seviceWorkerID is corresponding to the ServiceWorkerVersionId in Chromium
and it's zero-based number (-1 is used as an invalid number[1]).

[1]
https://code.google.com/p/chromium/codesearch#chromium/src/content/common/ser...

+    if (m_documentLoader)
+        return localFrame->loader().client()->serviceWorkerID(*m_documentLoader);
+    // m_documentLoader is null while loading resources from the imported HTML.
+    // In such cases a service worker ID could be retrieved from the document
+    // loader of the frame.
+    ASSERT(localFrame->loader().documentLoader());
+    return localFrame->loader().client()->serviceWorkerID(*localFrame->loader().documentLoader());
+}
+
 bool ResourceFetcher::shouldLoadNewResource(Resource::Type type) const
 {
     if (!frame())
         return false;
     if (!m_documentLoader)
         return true;
     if (type == Resource::MainResource)
         return m_documentLoader == frame()->loader().provisionalDocumentLoader();
     return m_documentLoader == frame()->loader().documentLoader();
 }
@@ skipping 907 matching lines @@
 
 void ResourceFetcher::trace(Visitor* visitor)
 {
     visitor->trace(m_document);
     visitor->trace(m_loaders);
     visitor->trace(m_multipartLoaders);
     ResourceLoaderHost::trace(visitor);
 }
 
 }